1. Field of the Invention
The present invention relates to a diaphragm valve; and more particularly relates to a diaphragm valve having a weir.
2. Brief Description of Related Art
Historically, a mix of flat surfaces with filleted corners and compound curves have combined to form the valve body and diaphragm interface. Difficulties arise in valve sealing when the shape of the diaphragm must conform to geometric variations that arise from processing the diaphragms and/or valve bodies. In addition, the inversion of the diaphragm that is required to open and close the valve induces significant stress to the diaphragm, when corners and multiple thickness sections are present.
FIG. 1 shows a known weir valve having a valve body (1) and a typical Polytetrafluoroethylene (PTFE) diaphragm (2) which has a thick section or boss (2a) where an attachment stud (3) is embedded into the thick PTFE part (2a). The valve body (1) has a weir section (1a) with a bottom portion that is typically flat. The weir section (1a) also has a curved section (1b) and two fillets (1c) that are in a transition area between the center and a flanged section (1d). The diaphragm (2) in the closed position must match the complex weir geometry. When the weir valve is opened, the diaphragm (2) is pulled up, and the curved section matching the curved section (1b) reverses it's shape. Diaphragm deformation and stress are concentrated in the tight radius section (2b) which, when closed, meet the body filleted sections (1c).
The complex weir surface is also difficult to measure or gauge. Combined with hand polishing, there is likely inconsistency from one valve to another in weir shape. Inconsistency must be compensated by greater sealing force applied by the actuator, resulting in reduced sealing efficiency. This also results in greater variability to the required seal pressure. The higher actuator force needed to insure that all diaphragms seal results in increased diaphragm wear and shorter diaphragm life. It also requires more powerful actuation and supporting structure within the valve design.
In FIG. 1, the diaphragm valve also has some other known components, parts or elements, including a backing cushion (4) arranged on the diaphragm (2), a compressor (5) arranged on the backing cushion (4), a tube nut (6) arranged in the compressor (5) and coupled to the attachment stud (3), a spindle flange (7) also arranged in the compressor (5), a spindle (8) arranged in the spindle flange (7) and a bonnet portion (9) for coupling to the valve body (1), as shown.
See U.S. Pat. No. 3,310,281, which discloses a diaphragm valve having an opening surrounded by a rim which has a surface lying in a flat plane, and also having a weir that provides on its top surface a narrow band seating which is concave with respect to the top plane, has a generally straight center portion, and has curved end portions turning upward from ends of the generally straight center portion and then curving over the other way to blend smoothly and gradually with a rim surface, as described in column 5, the last two paragraph (lines 53-75). In U.S. Pat. No. 3,310,281, the narrow band seating is not disclosed as being circularly-shaped in two-dimensions or spherically-shaped in three dimensions.